WO2018162393A1

WO2018162393A1 - Vinpocetine co-crystals and preparation process thereof

Info

Publication number: WO2018162393A1
Application number: PCT/EP2018/055314
Authority: WO
Inventors: Barbara PACCHETTI; Andrea Mereu; Giuseppe Paladino
Original assignee: Linnea Sa
Priority date: 2017-03-07
Filing date: 2018-03-05
Publication date: 2018-09-13
Also published as: IT201700025273A1

Abstract

The present invention relates to vinpocetine resorcinol co-crystals, and to a process for the preparation thereof.

Description

VINPOCETINE CO-CRYSTALS AND PREPARATION PROCESS

THEREOF

FIELD OF THE INVENTION The present invention relates to vinpocetine resorcinol co-crystals, and to a process for the preparation thereof.

BACKGROUND OF THE INVENTION

Vinpocetine is a derivative of the alkaloid vincamine. Vincamine is found in the aerial part of Vinca minor plant and can also be derived from other plant sources such as the Voacanga and the Crioceras Longiflorus. The Vinca minor plant is a creeping root plant which has a long history of use as a traditional tonic to refresh weariness, especially the type associated with advanced age, and also as an astringent, for excessive menses, bleeding gums and mouth sores. Vinpocetine is the active ingredient of Cavinton and Intelectol. Vinpocetine is held to exhibit an activity on neuronal metabolism by favoring the aerobic glycolysis and promoting the redistribution of the blood flow towards ischemic areas. Vinpocetine is also reported to act to increase cerebral circulation and the use of oxygen. Vinpocetine is commonly used as an aid to improving memory, as an aid in activities requiring highly focused attention and concentration such as technical writing or computer operation and to combat the symptoms of senile dementia. Vinpocetine has also been reported as showing promising results in the treatment of tinnitus or ringing in the ears as well as other causes of impaired hearing. Vinpocetine is also indicated in the treatment of strokes, menopausal symptoms and macular degeneration. Literature suggests vinpocetine may also act to improve conditions related to insufficient blood flow to the brain including vertigo and Meniere's disease, difficulty in sleeping, mood changes and depression.

Vinpocetine is represented by the following formula (I). The chemical name of vinpocetine is (3a,16a)-eburnamenine-14-carboxylic acid ethyl ester. Apovincamine is the corresponding methyl ester of the (3a, 16a)- eburnamenine-14-carbox lic acid.

Active pharmaceutical ingredients (API's) which, like vinpocetine, are generally less water soluble and less bioavailable create huge problems for the pharmaceutical industry. Research has shown that some drug candidates fail in the clinical phase due to poor human bioavailability and problems with the formulation. Traditional methods to address these problems, without completely redesigning the molecule, include salt selection, producing amorphous material, particle size reduction, pro-drugs, and different formulation approaches. Some attempts to use such techniques with vinpocetine are described, for example, in EP0154756B1 and EP0689844A1 .

Although therapeutic efficacy is the primary concern for an API, the salt and solid state form (i.e., the crystalline or amorphous form) of a drug candidate can be critical to its pharmacological properties and to its development as a viable API. Recently, crystalline forms of API's have been used to alter the physicochemical properties of a particular API. Each crystalline form of a drug candidate can have different solid state (physical and chemical) properties. The differences in physical properties exhibited by a novel solid form of an API (such as a co-crystal or polymorph of the original therapeutic compound) affect pharmaceutical parameters such as storage stability, compressibility and density (important in formulation and product manufacturing), and solubility and dissolution rates (important factors in determining bioavailability). Because these practical physical properties are influenced by the solid state properties of the crystalline form of the API, they can significantly impact the selection of a compound as an API, the ultimate pharmaceutical dosage form, the optimization of manufacturing processes, and absorption in the body. Moreover, finding the most adequate solid state form for further drug development can reduce the time and the cost of that development.

Obtaining crystalline forms of an API is extremely useful in drug development. It permits better characterization of the drug candidate's chemical and physical properties. It is also possible to achieve desired properties of a particular API by forming a co-crystal of the API and a co- former. Crystalline forms often have better chemical and physical properties than the free base in its amorphous state. Such crystalline forms may, as with the co-crystals of the invention, possess more favorable pharmaceutical and pharmacological properties or be easier to process than known forms of the API itself. For example, a co-crystal may have different dissolution and solubility properties than the API itself and can be used to deliver APIs therapeutically. New drug formulations comprising co-crystals of a given API may have superior properties over its existing drug formulations. They may also have better storage stability.

Another potentially important solid state property of an API is its dissolution rate in aqueous fluid. The rate of dissolution of an active ingredient in a patient's stomach fluid may have therapeutic consequences since it impacts the rate at which an orally administered active ingredient may reach the patient's bloodstream.

A co-crystal of an API is a distinct chemical composition of the API and co- former and generally possesses distinct crystallographic and spectroscopic properties when compared to those of the API and co-former individually. Crystallographic and spectroscopic properties of crystalline forms are typically measured by X-ray powder diffraction (XRPD) and single crystal X-ray crystallography, among other techniques. Co-crystals often also exhibit distinct thermal behavior, usually measured in the laboratory by differential scanning calorimetry (DSC). Stoichiometry of the API and co-former within the co- crystal can be confirmed by H NMR technique.

Co-crystals are generally defined as homogeneous crystalline structures comprising two or more components that can be atoms or molecules in a definite stoichiometric ratio. Contrary to salts, where the arrangement in the crystal lattice is based on ion pairing, the components of a co-crystal structure interact via non-ionic and also non-covalent weak intermolecular interactions such as hydrogen bonding, van der Waals forces and ττ-interactions.

SUMMARY OF THE INVENTION

The Applicant has faced the problem of finding stable co-crystalline forms of vinpocetine with the aim of improving the chemical and physical properties of vinpocetine.

After extensive investigation, the Applicant has found a stable co-crystalline form of vinpocetine with resorcinol as co-former, and a process for the consistent and reproducible preparation thereof.

Accordingly, a first aspect of the present invention is a co-crystalline form of vinpocetine and resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1.

For sake of clarity, the "co-crystalline form of vinpocetine and resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 " according to the present invention will be referred to as "Form A" for the purpose of the present description and appended claims.

The Form A can be characterized by a X-ray powder diffraction pattern having detectable peak(s) at 7.5°; 10.1 °; 13.4°; 15.7°; 17.6°; 18.9°; and 22.8° (2-Theta, ±0.1 ). Furthermore, the Form A can be characterized by a XRPD pattern substantially as depicted in Figure 1 .

Alternatively, the Form A can be characterized by a DSC profile having an endothermic peak at 1 1 1.94°C ± 1 °C with an onset at 1 1 1 .00°C ± 1 °C Furthermore, the Form A can be characterized by a DSC profile substantially as depicted in Figure 2.

As a further alternative, the Form A can be characterized by a ¹H NMR spectrum substantially as depicted in Figure 3(a) and by a ¹³C NMR spectrum substantially as depicted in Figure 3(b).

A second aspect of the present invention is a process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 (Form A) comprising the following steps:

• dispersing vinpocetine and resorcinol in a solvent, wherein said solvent is selected from the group of xylene, toluene, heptane and any mixture thereof,

• stirring and heating at a temperature below the boiling point of said solvent the resulting dispersion until complete dissolution,

• cooling the solution at a temperature ranging from 0°C to 30°C,

• stirring the resulting dispersion for a time equal to or higher than 5 hours,

• separating the solid from the dispersion, and

• washing and drying the resulting solid, wherein the resulting solid is a co-crystalline form of vinpocetine and resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 .

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows an XRPD pattern for the 1 :1 vinpocetine and resorcinol co- crystals (Form A). Figure 2 shows a DSC profile for the 1 :1 vinpocetine and resorcinol co- crystals (Form A) .

Figure 3(a) shows a ¹H NMR spectrum in solution of 1 :1 vinpocetine and resorcinol co-crystals (Form A). Figure 3(b) shows a solid state ¹³C NMR spectrum of 1 :1 vinpocetine and resorcinol co-crystals (Form A).

Figure 4 is a Cartesian graphic plotting the average HPLC area values of Form A and vinpocetine solubility against time as measured at room temperature in the solubility test example. Figure 5 is a Cartesian graphic plotting the average HPLC area values of Form A and vinpocetine solubility against time as measured at 37°C in the solubility test example.

Figure 6 is a Cartesian graphic plotting the average HPLC area values of Form A and vinpocetine solubility against time as measured at room temperature and at 37°C in the solubility test example.

DETAILED DESCRIPTION OF THE INVENTION

The Form A according to the present invention can be characterized by a X-ray powder diffraction (XRPD) pattern having detectable peak(s) at 7.5°; 10.1 °; 13.4°; 15.7°; 17.6°; 18.9°; and 22.8° (2-Theta, ±0.1 ).

The Form A according to the present invention can be further characterized by a XRPD pattern having one or more additional detectable peak(s) selected from the peaks at 12.8°; 13.7°; 13.8°; 15.0°; 20.4°; 20.7°; and 24.4° (2-Theta, ±0.1 ).

Furthermore, the Form A according to the present invention can be further characterized by a XRPD pattern having one or more additional detectable peak(s) selected from the peaks at 16.4°; 19.7°; 20.9°; 23.5°; 23.7°; and 26.3° (2-Theta, ±0.1 ). Furthermore, the Form A can be characterized by a XRPD pattern substantially as depicted in Figure 1.

Diffraction measurement was performed at ambient conditions on a PANalytical X'Pert PRO Θ-Θ diffractometer of 240 mm of radius in reflection geometry, equipped with Cu Ka radiation and a PIXcel detector, operated at 45 kV and 40 mA. The sample was mounted on a zero background silicon sample holder and allowed to spin at 0.25 rev/s during the data collection. The measurement angular range was 3.0-40.0° (2Θ) with a step size of 0.013°. The scanning speed was 0.0827s (40.8 s/step). Alternatively, the Form A of the present invention can be characterized by a DSC profile having an endothermic peak at 1 1 1.94°C ± 1 °C with an onset at 1 1 1 .00°C ± 1 °C. Furthermore, the Form A can be characterized by a DSC profile substantially as depicted in Figure 2.

DSC analysis was performed with a Mettler-Toledo TGA/DSC-2 Thermogravimetric Analyzer equipped with STAR^e software version 13.00. The sample under examination was heated at 10°C/min from 25 to 300°C under a nitrogen flow of 50 mL/min.

As a further alternative, the Form A of the invention can be characterized by a ¹H NMR spectrum in solution substantially as depicted in Figure 3(a) and by a solid state ¹³C NMR spectrum substantially as depicted in Figure 3(b).

Proton nuclear magnetic resonance analysis was recorded in deuterated methanol (CD₃OD) in a Varian Mercury 400 spectrometer, equipped with a broadband probe ATB 1 H/19F/X of 5 mm. The spectrum was acquired dissolving 5 mg of the sample under examination in 0.6 mL of the deuterated solvent.

Solid state ¹³C NMR measurements were carried out on a Bruker AVANCE 500 spectrometer. The compound was grinded up with a mortar and pestle and packed in cylindrical 4 mm outer diameter zirconia rotors, with sample volume of 80 μΙ_. Spectra were recorded at 34°C at the spinning speed of 12 kHz.

The skilled person will understand that the graphical representations of Figures 1 to 3 are generally influenced by factors such as variations in sample preparation and purity and variations in instrument response, which may result in small variations of peak intensities and peak positions. Nevertheless, the person skilled in the art would be readily capable of evaluating whether two sets of data are identifying the same crystal form or two different forms by comparing the graphical data disclosed herein with graphical data generated for a comparison sample. Therefore, the term "substantially as depicted in Figure 1 (or 2 or 3)" includes crystalline forms characterized by graphical data with small variations well known to the skilled person.

The term "detectable peak", as used herein, denotes that the peak in the XRPD pattern has a signal-to-noise (S/N) ratio equal or higher than 3.0. Signal-to-noise ratio of a peak is a dimensionless parameter that is calculated by dividing the height of the peak by the baseline width of the diffraction plot, both expressed using the same length units (e.g. mm). The height of a peak is calculated by measuring the distance between peak's maximum and the baseline of the peak. Peak's maximum 2-theta values are identified by having a first-derivative value equal to zero, and a negative second-derivative value. The baseline of the peak is obtained by tracing a straight line which is tangent to the diffraction plot at the closest 2-theta value which is lower than peak's maximum 2-theta value and has both first- and second-derivative values equal to zero, and also tangent to the diffraction plot at the closest 2-theta value which is higher than peak's maximum 2-theta value and has both first- and second-derivative values equal to zero. The height of the peak is obtained by tracing a second straight line which is parallel to the previously obtained baseline of the peak and tangent to the diffraction plot at the peak's maximum 2-theta value, and measuring the distance (perpendicularly to the X-axis of the diffraction plot) between both parallel lines. On the other hand, the baseline width of the diffraction plot is calculated by tracing two parallel lines to the X- axis of the diffraction plot, the first line being tangent to the diffraction plot at its maximum value in the range between 45° and 50° (2-theta), and the second line being tangent to the diffraction plot at its minimum value in the same range between 45° and 50° (2-theta), and measuring the perpendicular distance between both parallel lines.

According to the second aspect of the present invention, the stable co- crystalline form of vinpocetine with resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 (Form A) can be obtained with a preparation process comprising the following steps:

stirring and heating at a temperature below the boiling point of said solvent the resulting dispersion until complete dissolution, cooling the solution at a temperature ranging from 0°C to 30°C, stirring the resulting dispersion for a time equal to or higher than 5 hours,

separating the solid from the dispersion, and

Preferably, the solvent is selected from xylene and a mixture of toluene and heptane, having preferably a toluene:heptane weight ratio of from 9:1 to 1 :1 , and more preferably from 5:1 to 1 :1. Most preferably, the mixture of toluene and heptane has toluene:heptane weight ratio of from 4:1 to 1.5:1.

Advantageously, the solution is cooled at a temperature ranging from 0°C to 25°C, and more preferably ranging from 0°C to 20°C. Most preferably, the solution is cooled at a temperature ranging from 0°C to 10°C.

During the cooling step, the solution is preferably seeded with Form A to promote the formation of co-crystals. The addition is preferably made at a temperature below 80°C, preferably below 60°C.

Particularly, the resulting dispersion is stirred for a time ranging from 5 to 30 hours, preferably from 10 to 25 hours, and most preferably from 15 to 20 hours.

The Form A according to the present invention shows superior stability and solubility. In particular it is stable without giving rise to by-products for at least 18 months under the conditions defined for long term stability under the ICH guidelines.

The Form A is therefore particularly suitable for the use in the pharmaceutical field, as well as in the non-pharmaceutical field, as supplement and/or nutraceutical. Accordingly, this invention further encompasses a pharmaceutical composition comprising the Form A, as described above, and at least one pharmaceutically acceptable excipient, and a process for the preparation of such a pharmaceutical composition by combining the Form A, as described above, and at least one pharmaceutically acceptable excipient.

At the same time, this invention further encompasses supplement and/or nutraceutical compositions comprising the Form A, as described above, and at least one edible excipient.

The term "pharmaceutically acceptable excipient" is understood to comprise without any particular limitations any material which is suitable for the preparation of a pharmaceutical composition which is to be administered to a living being. Depending upon the role performed, excipients are classified into (i) filler excipients, (ii) production excipients, (iii) preservative excipients, and (iv) presentation excipients. These materials, which are known in the art, are for example (i) diluents, absorbents, adsorbents, fillers and humectants, (ii) lubricants, binders, glidants, plasticizers and viscosity modifiers, (iii) preservatives, antimicrobials, antioxidants and chelating agents, and (iv) flavorings, sweeteners and coloring agents.

The Form A and the pharmaceutical composition containing it can be used as a medicament, supplement, or nutraceutical, for example as an aid to improve memory, to combat the symptoms of senile dementia, and to improve conditions related to insufficient blood flow to the brain.

For better illustrating the invention the following non-limiting examples are now given.

EXAMPLE 1

Vinpocetine base (6.50 g, 18.61 mmol, 1.2 eq.) and resorcinol (1.7 g, 15.52 mmol) were suspended in xylene (33 mL) in a 3-necked 100 ml round- bottomed flask, equipped with mechanical stirring. The resulting suspension was heated until complete dissolution at 120°C affording a yellow solution. The solution was slowly cooled and was seeded at 57°C with Form A. Then the mixture was stirred at room temperature for 15 hours and at 0°C for 2 hours. Finally the resulting suspension was filtered through a sinter funnel (porosity n°3), washed with 2 x 6.5 mL of cold xylene and 2 x 6.5 mL of cold heptane and dried under vacuum at room temperature giving 1 :1 vinpocetine and resorcinol co-crystal as an off-white solid (6.35 g, 89%). Residual xylene or heptane were not detectable by ¹H NMR.

EXAMPLE 2

The same procedure of example 1 was repeated by using a slightly lower amount of vinpocetine (5.96 g, 17.06 mmol, 1.1 eq.) and the same amount of resorcinol (1.7 g, 15.52 mmol) suspended in toluene (33 mL) and heating at 90°C, so obtaining 4.21 g of 1 :1 vinpocetine and resorcinol co-crystal (yield 59%). EXAMPLE 3

The same procedure of example 1 was repeated by using the same amount of vinpocetine base (6.50 g, 18.61 mmol, 1.2 eq.) and resorcinol (1 .7 g, 15.52 mmol) suspended in a mixture toluene/heptane 8/2 (33 ml_), heating at 90°C, and omitting the stirring at 0°C, so obtaining 3.14 g of 1 :1 vinpocetine and resorcinol co-crystal (yield 44%).

EXAMPLE 4

The same procedure of example 1 was repeated by using the same amount of vinpocetine base (6.50 g, 18.61 mmol, 1.2 eq.) and resorcinol (1 .7 g, 15.52 mmol) suspended in a mixture toluene/heptane 6/4 (33 ml_), heating at 90°C, and omitting the stirring at 0°C, so obtaining 4.85 g of 1 :1 vinpocetine and resorcinol co-crystal (yield 68%).

EXAMPLE 5

The same procedure of example 1 was repeated by using the same amount of vinpocetine base (6.50 g, 18.61 mmol, 1.2 eq.) and resorcinol (1 .7 g, 15.52 mmol) suspended in a mixture toluene/heptane 6/4 (33 ml_), heating at 90°C, so obtaining 5.85 g of 1 :1 vinpocetine and resorcinol co-crystal (yield 82%).

EXAMPLE 6 Vinpocetine base (19.5 g, 55.6 mmol, 1 ,2 eq.) and resorcinol (5.1 g, 46.3 mmol) were suspended in xylene (100 mL) in a 3-necked 100 ml round- bottomed flask, equipped with mechanical stirring.

The resulting suspension was heated until complete dissolution at 120°C affording a yellow solution. The solution was slowly cooled and was seeded at 57°C with Form A. Then the mixture was stirred at room temperature for 15 hours and at 0°C for 2 hours. Finally the resulting suspension was filtered through a sinter funnel (porosity n°3), washed with 2 x 20 mL of cold xylene and 2 x 20 mL of cold heptane and dried under vacuum at room temperature giving 1:1 vinpocetine and resorcinol co-crystal as an off-white solid (9.5 g, 91%). Residual solvents: Xylene 74 ppm, heptane 11 ppm. HPLC assay 98.2%. Co-crystal structure was confirmed by solid state ¹³C-NMR and XRDP.

COMPARATIVE EXAMPLE 1

5 Several experiments with different solvents or solvent mixtures, different stoichiometry between vinpocetine (VNP) and resorcinol (RSC), and different techniques were conducted in order to obtain the co-crystalline form of vinpocetine and resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1:1 (Form A). The results are summarized in the following Table 1.0 TABLE 1

Technique Solvent Stoichiometry Result

VNP:RSC

Crystallization EtOAc, MIK, MTBE 1:5 VNP + RSC

Precipitation EtOAc, MIK, Et₂0, ACN, 1:1, 1:2, 1:5, 1:6 VNP + RSC acetone, TCM

Slurrying THF, EtOH, IPA, iBuOAc, 1:1, 1:3, 1:5, 2:1 VNP + RSC

MTBE, MeOH, ACN,

acetone, DCM, toluene,

cyclohexane

Slurrying H₂0, MTBE, THF/H₂01:1, 1:6 Form A + VNP

THF/H2O 1:3, dioxane/H₂0

1:3, acetone/H₂01:1,

acetone/H₂01 :3

Slurrying MEK, MIK, MIK/H₂01:1, 1:1, 1:3, 1:6 VNP

MEK/H₂01:1, MIK/H₂01:3,

dioxane/H₂01:1

Wet grinding MeOH, toluene, DMF 1:1, 1:2, 1:3, VNP + RSC

1:5, 2:1, 3:1

Wet grinding water, THF, TCM and ACN 1:5 Form A + VNP

Wet grinding Acetone 1:5 Form A + VNP

Slow evaporation THF 1:1 Form A MeOH : methanol MTBE : Methyl tert-butyl ether

EtOH : ethanol THF : Tetrahydrofuran

EtOAc : Ethyl acetate I PA : Isopropyl alcohol

iBuOAc : iso-butyl acetate ACN : acrylonitrile

MEK : Methyl ethyl ketone DMF : dimethylformamide

MIK : Methyl Isobutyl ketone TCM : chloroform

Et₂0 : Ethyl ether DCM : methylene chloride

The results of the above experiments provided the conclusion that Form A could be obtained only with a specific combination of technique, solvent and stoichiometry. For example, it is worth noting that a solvent useful with a technique, such as for example toluene with crystallization, as described in example 2, does not provide any result when employed with another technique, such as for example slurrying or wet grinding.

Further, most tested solvents or mixture of solvents do not provide any result with any technique, irrespective of the stoichiometry of vinpocetine and resorcinol.

Some solvents or mixture of solvents provide some results with some technique when used with an excess of resorcinol (stoichiometry 1 :5 or 1 :6), but this would require several washing steps to eliminate such an excess of resorcinol, leading to a partial dissociation of the co-crystal affording traces of vinpocetine base and low yield (as low as 10%).

Finally, the result obtained with slow evaporation from THF can be reproduced in laboratory only and has not industrial applicability.

COMPARATIVE EXAMPLE 2 Several experiments with different solvents (H₂0, MeOH, EtOH, EtOAc, iBuOAc, acetone, MEK, MIK, Et₂0, THF, dioxane, toluene, cyclohexane, IPA, ACN, DMF, MTBE, TCM, and DCM), different stoichiometry between vinpocetine and co-former (1 :1 , 2:1 , 1 :2, 1 :3, 1 :4 and 1 :5), and different techniques (slurrying, grinding, crystallization, precipitation, slow evaporation) were conducted in order to identify further co-crystals of vinpocetine with different co-formers, as listed in the following Table 2.

TABLE 2

The results of such an extensive experimentation provided the conclusion that vinpocetine did not form a co-crystal with any of the co-formers listed in the above Table 2 in any solvent with any technique and stoichiometry.

SOLUBILITY TEST A comparative solubility study of the co-crystalline form of vinpocetine and resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 (Form A) and vinpocetine free base crystals (VNP) was performed in a phosphate buffer at pH equal to 6.8 at room temperature and at 37°C. The buffer solution was prepared according to USP 35-NF 30 but more concentrated (0.15 M instead of 0.05 M) in order to maintain the buffer effect.

As vinpocetine coming from the dissociation of Form A could re-precipitate (due to a possible "spring and parachute" effect - Warren et al., "Using polymeric precipitation inhibitors to improve the absorption of poorly water- soluble drugs: A mechanistic basis for utility". Journal of Drug Targeting, 2010; 18(10): 704-731 ), samples were taken at different times (0.25, 1 , 2, 4, 5 and 24 h) in order to determine the kinetic solubility profile. The "spring" solubility profile is due to the rapid dissolution of the vinpocetine during the dissociation of the Form A. Then the "parachute" solubility profile is due to the progressive re-precipitation of the oversaturated vinpocetine in the medium.

The relative solubility of vinpocetine has been directly obtained by comparison of the area of vinpocetine peak in the HPLC analyses of direct samples taken from the filtrate of a dispersion of vinpocetine free base crystals and a dispersion of the Form A in the corresponding media. Solubility tests were performed in a minireactor HME-R, provided with a 250 mL vessel, a temperature sensor and mechanical stirring. Form A and vinpocetine free base crystals were previously ground with a mortar in order to limit a particle size effect. Then, 1 g of each material was stirred in the aqueous buffer solution (150 mL, 15 V) under the same conditions of stirring speed (mechanical stirring at 350 rpm in order to have a good dispersion of the solid in the medium). Aliquots of ca. 5 mL of suspension were filtered in a sintered glass funnel (#4) at different times: 15, 60, 120, 240, 300 min and 24 h. After filtration, pH of the mother liquor was determined and 1 mL of it was filtered through 0.45 μηη nylon filters and directly analyzed by HPLC (2 injections for each sample).

In the case of Form A, the filtered solid was analyzed by XRPD, without a drying step. These analyses allowed to evaluate whether the measured solubility corresponds to Form A, a mixture of re-precipitated vinpocetine and Form A or only to re-precipitated vinpocetine. The selected conditions to determine the solubility of vinpocetine were the following:

Column: Luna C18, 250 x 4.6 mm, 5 μηη

Mobile phase: A: ACN

B: 15.4 g/L (0.2 M) aqueous ammonium acetate Isocratic 70% A : 30% B

Temperature: room temperature

Flow rate: 1 mL/min

UV detector wavelength: 280 nm

Injection: 15 μΙ_

Run time: 20 min

The results of the solubility studies at room temperature (ca. 25±1°C) and at 37±1 °C in a pH 6.8 buffer solution are shown in the following Tables 3 and 4. The average HPLC area values against time were also plotted and represented in Figures 4 and 5.

TABLE 3 - Room temperature

TABLE 4 - Temperature 37°C

Average HPLC vinpocetine area from:

Time

Form A Vinpocetine crystals

15 min 40.181 23.868

1 hour 22.576 25.433 2 hours 20.999 26.440

4 hours 23.207 21 .843

5 hours 17.812 23.935

24 hours 22.41 1 22.937

At room temperature, a clear "spring and parachute" effect is clearly visible due to the dissolution of vinpocetine from Form A and its subsequent re- precipitation as crystalline vinpocetine. After 1 h, only traces of Form A remain in the solid suspension. The solubility of Form A is clearly higher than that of vinpocetine crystals during the first 60 minutes (by factors of 2.3-1.7). Then the solubility of Form A decreases gradually to reach the solubility of vinpocetine after about 2 hours.

At 37°C, a similar "spring and parachute" effect due to dissolution of vinpocetine from of Form A and its subsequent re-precipitation as crystalline vinpocetine is visible during the first hour. As in the case of the solubility test at room temperature, such an improvement of solubility is due to the dissociation of Form A. However, the dissociation is clearly faster at 37 °C than at room temperature.

In order to monitor the dissolution trend during the first hour, the solubility test of Form A at 37°C was repeated with a shorter check time (every 5 minutes). The results are shown in the following Table 5. The average HPLC area values against time were also plotted and represented in Figure 6, together with the previous results of dissolution of Form A at room temperature (Table 3).

TABLE 5

Average HPLC vinpocetine

Time

area from Form A

5 min 48.578 10 min 41 .697

15 min 31 .441

20 min 24.638

25 min 20.667

30 min 26.503

35 min 25.944

40 min 24.365

45 min 22.284

50 min 19.325

55 min 14.928

60 min 15.521

180 min 20.678

24 h 26.143

The comparison illustrated in Figure 6 clearly showed a "spring and parachute" effect in both cases due to the dissociation of Form A, confirming that at 37°C the dissociation of Form A is faster and the "spring and parachute" effect is less intense.

STABI LITY TEST

A sample of Form A was stored at 25°C ± 2°C/60 % RH ± 5% RH for long term stability studies according to ICH guideline.

The sample were analyzed at release and after 3, 6, 12 and 18 months. The crystalline Form A was found stable after 18 months as XRDP remained unchanged over time. The product was also analyzed by HPLC purity and assay, KF water and GC solvent content, resulting chemically stable after 18 months storage.

Claims

1. A co-crystalline form of vinpocetine and resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 (Form A).

2. The co-crystalline form of vinpocetine and resorcinol according to claim 1 , characterized by a X-ray powder diffraction (XRPD) pattern having detectable peak(s) at 7.5°; 10.1 °; 13.4°; 15.7°; 17.6°; 18.9°; and 22.8° (2- Theta, ±0.1 ).

3. The co-crystalline form of vinpocetine and resorcinol according to claim 2, characterized by a XRPD pattern having one or more additional detectable peak(s) selected from the peaks at 12.8°; 13.7°; 13.8°; 15.0°; 20.4°; 20.7°; and 24.4° (2-Theta, ±0.1 ).

4. The co-crystalline form of vinpocetine and resorcinol according to claim 3, characterized by a XRPD pattern having one or more additional detectable peak(s) selected from the peaks at 16.4°; 19.7°; 20.9°; 23.5°; 23.7°; and 26.3° (2-Theta, ±0.1 ).

5. The co-crystalline form of vinpocetine and resorcinol according to any one of the preceding claims 1 to 4, characterized by a DSC profile having an endothermic peak at 1 1 1.94°C ± 1 °C with an onset at 1 1 1.00°C ± 1 °C.

6. The co-crystalline form of vinpocetine and resorcinol according to any one of the preceding claims 1 to 4, characterized by a NMR spectrum substantially as depicted in Figure 3(a) or 3(b).

7. A process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol having a molar ratio of vinpocetine to resorcinol equal to 1 :1 (Form A) comprising the following steps:

• dispersing vinpocetine and resorcinol in a solvent, wherein said solvent is selected from the group of xylene, toluene, heptane and any mixture thereof, • stirring and heating at a temperature below the boiling point of said solvent the resulting dispersion until complete dissolution,

• cooling the solution at a temperature ranging from 0°C to 30°C,

• separating the solid from the dispersion, and

8. The process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol according to claim 7, characterized in that said solvent is selected from xylene and a mixture of toluene and heptane.

9. The process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol according to claim 8, characterized in that said mixture of toluene and heptane shows a toluene:heptane weight ratio of from 9:1 to 1 : 1 , preferably from 5:1 to 1 :1 , and more preferably from 4:1 to 1.5:1.

10. The process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol according to claim 7, characterized in that said solution is cooled at a temperature ranging from 0°C to 25°C, preferably ranging from 0°C to 20°C, and more preferably ranging from 0°C to 10°C.

1 1. The process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol according to claim 7, characterized in that during the cooling step, the solution is seeded with Form A.

12. The process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol according to claim 1 1 , characterized in that said seeding of Form A is made at a temperature below 80°C, preferably below 60°C.

13. The process for the preparation of a stable co-crystalline form of vinpocetine with resorcinol according to claim 7, characterized in that said dispersion is stirred for a time ranging from 5 to 30 hours, preferably from 10 to 25 hours, and more preferably from 15 to 20 hours.

14. A pharmaceutical composition comprising the Form A, as described in any one of the preceding claims 1 to 6, and at least one pharmaceutically acceptable excipient.

15. A supplement or nutraceutical composition comprising the Form A, as described in any one of the preceding claims 1 to 6, and at least one edible excipient.